Fatigue Assessment for Bulk Carrier

According to the CSR

Student: Akram Madi

Supervisor: Dr. Maciej Taczala

O U T L I N EO U T L I N EO U T L I N EO U T L I N E

Fatigue–BK-CSR

Objectives & Methodology

Fatigue Assessment Hypothesis

Bulk Carrier Descriptions

Poseidon Global FEM-Model

ANSYS Global FEM-ModelANSYS Global FEM-Model

Submodelling

Hot spot Extrapolation & SCF

Cumulative Fatigue Damage

Conclusion and Recommendation

ObjectivesObjectivesObjectivesObjectives

Develop Global FEM under CSR

Develop submodels for evaluating the stress

concentration factor (SCF)

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concentration factor (SCF)

Assess the fatigue strength according to CSR

METHODOLOGYMETHODOLOGYMETHODOLOGYMETHODOLOGY

Literature Review

Rules of Classification Societies (CSR)

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FEM Software (Ansys – Poseidon)

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Fatigue Assessment HypothesisFatigue Assessment HypothesisFatigue Assessment HypothesisFatigue Assessment Hypothesis

•• Design SDesign S--N curvesN curves

•• Representation of long term distribution of stress Representation of long term distribution of stress

ranges by tworanges by two--parameters of Weibull probability parameters of Weibull probability

distributiondistribution

•• Minimum design life 25 years in North AtlanticMinimum design life 25 years in North Atlantic

•• PalmgrenPalmgren--Miner cumulative fatigue damageMiner cumulative fatigue damage

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FE Analysis FE Analysis FE Analysis FE Analysis ----Fatigue Assessment Fatigue Assessment Fatigue Assessment Fatigue Assessment

•• Dynamic fatigue loadsDynamic fatigue loads

Tuned on 10Tuned on 10--44 probability level, North Atlanticprobability level, North Atlantic

Load combination factorsLoad combination factors

•• Fatigue loads conditionsFatigue loads conditions•• Fatigue loads conditionsFatigue loads conditions

•• Model based on average (over life) corroded thickness, Model based on average (over life) corroded thickness, ttgrossgross –– 0.5 0.5 ttcorrcorr

• Hot spot stress calculated using very fine mesh (mesh size t x t)

Bulk CarrierBulk CarrierBulk CarrierBulk Carrier

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Length (o.a) Loa 190 m

Length (p.p) Lpp 182.6 m

Length scantling 180.72 m

Breadth (mld) 23.6 m

Specification Characteristics

Breadth (mld) 23.6 m

Depth (mld) 14.6 m

Draft (scantling) Tscan 10.1 m

Dead Weight 30000 t

Service Speed 14 kn

Bulk CarrierBulk CarrierBulk CarrierBulk Carrier

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Bulk CarrierBulk CarrierBulk CarrierBulk Carrier

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Poseidon Global FEM

Type of element: Shell element for plate and stiffeners

Extend of the model: 3 holds

Boundary Condition: simply supported

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Poseidon Global FEM

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Poseidon Global FEM

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Poseidon Global Mesh

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Homogenous Loading– H1

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ANSYS Global FEM

slave

points

master

point

MPC rigid

link/beam

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ANSYS Global FEM

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Structural Critical Detail

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Submodel

Procedures:

�Create and analyze the coarse model.

�Create the submodel.

�Perform the cut boundary interpolation�Perform the cut boundary interpolation

�Analyze the subomdel.�Verify the Distance Between the CB and area

of Stress Concentration is Adequate

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Hopper-IB Knuckle Submodel

Mesh Size:

txt (24x24 mm)

Mesh Type:

4 node shell Element

Load to GM:

Heavy Ballast

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Hopper-IB Knuckle Submodel

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Hopper-IB Knuckle Submodel

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Hopper-IB Knuckle Submodel

Hot Spot

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Hopper-IB Knuckle Sub model

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Hopper-IB Knuckle Sub model

Global ModelLocal Model

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Longitudinal-Web Frame Submodel

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Longitudinal-Web Frame Submodel

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Cumulative Fatigue Damage

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Cumulative Fatigue Damage

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Conclusions

Cumulative fatigue damage for Hopper-IB knuckle is less

than the limit criteria for fatigue damage and can survive up

Geometry SCF from direct FEM for longitudinal stiffener web

frame end connection depend on the geometry of structure

and load combination

Submodelling is significantly less time consuming nevertheless

efficient in getting reasonable result in the region of interest for

fatigue analysis

GL Poseidon Software for BC used as pre-processor for

modeling and ANSYS code as post-processor for fatigue

analysis is a very efficient

than the limit criteria for fatigue damage and can survive up

to 25 years in North Atlantic environment.

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Recommendations

Fatigue investigation to carry systematic identifications of error

sources in applying design loads and structural modeling and its

effect on the predicted fatigue damage

FE analysis using 8-node/or solid element for fatigue analysis for FE analysis using 8-node/or solid element for fatigue analysis for

these particular details can be done to compare with result from

the 4-node shell element

Different longitudinal stiffener web frame end connections geometries

can be analyzed for all loading conditions to obtain the combined

geometry stress concentration factors and presented as tabulated

reference in the rules.